The present invention relates to a new and distinct cultivar of Heuchera and given the cultivar name of ‘TNHEUNER’. Heuchera is in the family Saxifragaceae. Heuchera ‘TNHEUNER’ originated as a controlled cross using Heuchera ‘K797-3’, a proprietary, unpatented, unnamed plant as the seed parent, and Heuchera ‘K994-1’, a proprietary, unpatented, unnamed plant as the pollen parent. These parents are a result of breeding using hardy Heuchera richardsonii with proprietary hybrid lines. Heuchera ‘TNHEUNER’ was bred to be a hardy, large, landscape plant.
Compared to the seed parent, Heuchera ‘K797-3’, the new cultivar has a dark red to burgundy rather than brown leaves and gold rather than light pink flowers.
Compared to the pollen parent, Heuchera ‘K994-1’, the new cultivar has a larger habit.
Compared to Heuchera ‘Cherry Cola’, U.S. Plant Pat. No. 22,967, the new cultivar has a larger habit and larger leaves. The foliage of the new cultivar is dark red to burgundy colored rather than soft red. The flowers of the new cultivar are yellow green rather than rust red.
Compared to Heuchera ‘Root Beer’, U.S. Plant Pat. No. 23,173, the new cultivar has a larger habit and leaves. The foliage of the new cultivar is more intensely colored and less lobed.
This new Heuchera is uniquely distinguished by:                1. dark red to burgundy colored leaves,        2. medium size, slightly lobed, geranium-like leaves,        3. yellow green flowers in short spikes in spring,        4. good sun tolerance,        5. a medium large, mounding habit with excellent crown count, and        6. excellent vigor.        
This new cultivar has been reproduced only by asexual propagation (tip cuttings and tissue culture using growing tips). Each of the progeny exhibits identical characteristics to the original plant. Asexual propagation in 2013 by cuttings and tissue culture using standard micropropagation techniques with terminal and lateral shoots, as done in Canby, Oreg., shows that the foregoing characteristics and distinctions come true to form and are established and transmitted through succeeding propagations. The present invention has not been evaluated under all possible environmental conditions. The phenotype may change with variations in environment without a change in the genotype of the plant.